Keyword difficulty relates to the amount of competition there is for the keyword you are looking to rank for and is measured as a percentage (100% being the most difficult).
In the example used there Keyword difficulty is 44%. This shows that there are competitors also looking to rank for this term, but if you implement the correct strategy, you should be able to rank on the first page within a year.
When starting out, it can be a good idea to try and rank for keywords with very low difficulty. For example we can see here that “pension advice ireland” had a Keyword difficulty of 40%. This isn’t a huge difference, but doing this research may make a massive difference.